> We don't worry about people memorizing proprietary source code and "accidentally" using it

I'm not sure why it's different, but that's a common concern with music. For example: https://www.reddit.com/r/WeAreTheMusicMakers/comments/4v8u8d...

That's a really good observation. Perhaps it highlights an essential difference between two modes of thought - a fuzzy, intuitive, statistical mode based on previously seen examples, and a reasoned, analytical calculating mode which depends on a precise model of the system. Plausibly, the landscape of valid musical compositions is more continuous than the landscape of valid source code, and therefore more amenable to fuzzy, example-based generation; it's entirely possible to blend two songs and make a third song. Such an activity is nonsensical with source code, and so humans don't even try. We probably do apply that sort of learning to short snippets (idioms), but source code diverges too rapidly for it to be useful beyond that horizon.

This is not such a big problem in reality because the output of Copilot can be filtered to exclude snippets too similar to the training data, or any corpus of code you want to avoid. It's much easier to guarantee clean code than train the model in the first place.